Structure for bonding metal plate and piezoelectric body and bonding method

ABSTRACT

A bonding structure that provides excellent conductivity and bonding between a piezoelectric body and a metal plate includes a metal plate and an electrode of a piezoelectric body bonded to one another with an electrically conductive adhesive so as to provide electrical conductivity, the electrically conductive adhesive includes carbon black with a nano-level average particle size, and has a paste form included in a solventless or solvent-based resin so that the carbon black forms an aggregate with an average particle size of about 1 μm to about 50 μm. The electrically conductive adhesive is applied between the metal plate and the electrode of the piezoelectric body, and the metal plate and the piezoelectric body are subjected to heating and pressurization so that the carbon black aggregate is deformed, thereby hardening the electrically conductive adhesive.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a bonding structure for a metal plateand a piezoelectric body, such as a piezoelectric vibration plate foruse in a driver of a piezoelectric microblower or other suitablepiezoelectric device, and a bonding method therefor.

2. Description of the Related Art

Piezoelectric microblowers have been known as blowers for effectivelyreleasing heat produced in housings of portable electronic devices, oras blowers for supplying oxygen required for the generation ofelectricity in fuel cells (see, for example, WO2008/069266). Thepiezoelectric microblower refers to a kind of pump using a vibrationplate which produces a bending vibration by applying a voltage, and hasthe advantages of having a simple structure, being able to be configuredto have a small and thin size, and providing low power consumption.

FIG. 1 shows an example of a vibration plate for use in a piezoelectricmicroblower. In FIG. 1, a piezoelectric body (piezoelectric ceramicplate) 2 including electrodes 3, 4 on front and back sides thereof isbonded onto a metallic diaphragm 1. One electrode 3 and the diaphragm 1are electrically connected to each other. When a predeterminedalternating-current voltage is applied between the diaphragm 1 and theelectrode 4 of the piezoelectric body 2, the entire vibration plateproduces a bending vibration, thereby enabling it to pump the air. It isto be noted that the vibration plate is not limited to the piezoelectricbody 2 directly bonded onto the diaphragm 1, and may have variousconfigurations, such as a vibration plate which has another metal platebonded onto the diaphragm 1 and the piezoelectric body 2 bonded thereon,and a vibration plate which has a piezoelectric body 2 bonded onto bothof the front and back sides of the diaphragm 1.

FIGS. 2A to 2C show examples of a bonding structure between theelectrode 3 of the piezoelectric body 2 and the metal plate 1(diaphragm).

FIG. 2A is an example of using an adhesive 5 including no electricallyconductive aid, which is intended to provide electrical conductionthrough contact (ohmic contact) between the electrode 3 and the metalplate 1 by reducing the adhesive thickness between the piezoelectricbody 2 and the metal plate 1 to the greatest extent possible.

In FIG. 2B, carbon spheres 6 are added as an electrically conductive aidto the adhesive 5, thereby providing conductivity through the carbonspheres 6. The carbon spheres 6 have a diameter, for example, on theorder of 20 μm, and the electrode 3 is not directly connected to themetallic plate 1.

In FIG. 2C, carbon black 7 with an average particle size of several tensof nm is added as an electrically conductive aid to the adhesive 5,thereby providing conductivity through the carbon black 7 in addition toconductivity through contact between the electrode 3 of thepiezoelectric body 2 and the metal plate 1.

In the case of using the adhesive 5 including no electrically conductiveaid as shown in FIG. 2A, the problem of an increase in resistance value(a decrease in conductivity) is caused when the adhesive is swollen in ahumidity test after the bonding. In the case of using the adhesive 5with the carbon spheres 6 added thereto as in FIG. 2B, the piezoelectricbody 2 is likely to have cracks caused from the carbon spheres 6, andmoreover, the thickness of the adhesive is increased, thereby resultingin the problem of degraded vibration characteristics of thepiezoelectric body 2. In addition, the problem of increased resistancevalue is caused because of the contact with the electrode function aspoint contact, or because the largest particle functions as a spacer,whereas the smaller-size particles fail to contribute to electricalconduction. In the case of using the carbon black 7 with a minuteparticle size as in FIG. 2C, the viscosity-thixotropy of the adhesive isaffected significantly by the content of the carbon black 7, which hasthe problem of having an adverse effect on the workability andapplication property. Furthermore, the problem of an increase inresistance value (a decrease in conductivity) is also caused when theadhesive is swollen in a humidity test after the bonding.

Japanese Patent Application Laid-Open No. 2001-316655 discloses anelectrically conductive adhesive which is used for bonding between anactive material layer and a collector in an energy storage element. Thisadhesive is an electrically conductive adhesive in a paste form, whichincludes carbon powder (for example, carbon black) as an electricallyconductive material, a resin as a binding agent, and water as a solvent,in which primary particles of the carbon powder have a weight-averageparticle size in the range of 5 nm to 100 nm, the amount of the carbonpowder falls within the range of 5 weight % to 50 weight % with respectto the total amount of the carbon powder and resin, and the moisturecontent of the electrically conductive adhesive in the paste form issupposed to fall within the range of 70 weight % to 95 weight %.

FIG. 2D shows an example of a bonding structure using the electricallyconductive adhesive disclosed in Japanese Patent Application Laid-OpenNo. 2001-316655. As in the case of FIG. 2C, the carbon black 7 is addedas an electrically conductive aid to the adhesive 5, thereby providingconductivity through the carbon black 7 without direct electricalconduction between the electrode 3 and the metal plate 1. Since a largeramount of carbon black 7 is added than in FIG. 2C, the conductivity isbelieved to be improved more than in FIG. 2C.

However, when the carbon black 7 having a particle size of 5 nm to 100nm is contained in the resin in a large amount of weight % to 50 weight%, the viscosity or thixotropy of the adhesive is greatly increased soas to adversely affect the application stability (variations in theamount of application, leveling properties after the application).Therefore, this problem is solved by water (70 weight % to 95 weight %)included in the paste in Japanese Patent Application Laid-Open No.2001-316655. For this reason, it is not possible to solve the problemdescribed in the case of a reaction system (such as an epoxy resin)which does not use water. In addition, the larger content of the carbonblack 7 relatively reduces the amount of resin, thus decreasing theadhesion. Furthermore, the large amount of water included as a solventprovides a porous formation when the adhesive is hardened, therebyresulting in the problem of making the adhesive more likely to beswollen by absorption of water, and thus, lacking long-term reliability.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide a bonding structure and a bonding method whichhave excellent conductivity and bonding property between a piezoelectricbody and a metal plate.

A preferred embodiment of the present invention provides a bondingstructure that preferably includes a metal plate, a piezoelectric bodyincluding an electrode on the side opposed to the metal plate, and anelectrically conductive adhesive including carbon black as anelectrically conductive aid, and bonding the metal plate and theelectrode of the piezoelectric body so as to have electricalconductivity, wherein the electrically conductive adhesive beforehardening includes carbon black with a nano-level average particle size,and is a paste included in a solventless or solvent-based resin so thatthe carbon black provides an aggregate with an average particle size ofabout 1 μm to about 50 μm, for example, and wherein the bondingstructure is configured by applying the electrically conductive adhesivein the paste form between the metal plate and the electrode of thepiezoelectric body, subjecting the metal plate and the piezoelectricbody to heating, and pressurization to deform the carbon blackaggregate, and hardening the electrically conductive adhesive.

Another preferred embodiment of the present invention provides a bondingmethod in which a metal plate and a piezoelectric body including anelectrode on the side opposed to the metal plate are bonded to eachother via an electrically conductive adhesive including carbon black asan electrically conductive aid, so as to have electrical conductivitybetween the metal plate and the electrode of the piezoelectric body, andthe bonding method preferably includes the steps of applying theelectrically conductive adhesive in a paste form between the metal plateand the electrode of the piezoelectric body, which includes carbon blackwith a nano-level average particle size, and is included in asolventless or solvent-based resin so that the carbon black forms anaggregate with an average particle size of about 1 μm to about 50 μm,for example, and after applying the electrically conductive adhesive,subjecting the metal plate and the piezoelectric body to heating andpressurization to deform the carbon black aggregate, and hardening theelectrically conductive adhesive.

The electrically conductive adhesive preferably includes carbon blackwith a nano-level average particle size, and is a paste included in aresin so that the carbon black forms an aggregate with an averageparticle size of about 1 μm to about 50 μm, for example. The aggregaterefers to primary particles of the carbon black bonded by anintermolecular force or other relevant force to provide a cluster withan average particle size of about 1 μm or more, for example. Therefore,as compared to the same amount of carbon black included in a dispersedstate in a resin, the viscosity or thixotropy of the adhesive is muchless affected, thereby resulting in improved workability and applicationproperty. The aggregate itself has no rigidity, and is deformed tofollow a concavity and a convexity of the metal plate and piezoelectricbody when the metal plate and the piezoelectric body are subjected toheating and pressurization. Thus, conductivity can be provided with lessdamage to the piezoelectric body and without significantly contributingto an increase in the thickness of the adhesive. The electricalconductivity between the metal plate and the piezoelectric body canpreferably be achieved by not only the electrical conduction through thecarbon black, but also by direct contact between the metal plate and theelectrode of the piezoelectric body, thus providing a higher electricalconductivity (lower resistance value).

The average particle size in preferred embodiments of the presentinvention can preferably be obtained by, for example, capturing a SEMimage of powder, applying binarization processing to the obtained imageto obtain the area of the powder, and converting the area into circleswith a diameter. It is possible to capture SEM images of both primaryparticles and secondary particles.

The particle size of the aggregate preferably has a lower limit size ofabout 1 μm, for example, because the size less than about 1 μm greatlyincreases the resin viscosity, and on the other hand, the upper limitsize of greater than about 50 μm makes the size of the aggregate largerthan the concavity and convexity at the surfaces of the metal plate andelectrode, thus increasing the thickness of the adhesive. Therefore, theupper limit size is preferably about 50 μm, for example.

In a preferred embodiment of the present invention, the carbon black ispreferably hardened while remaining as the aggregate rather than in adispersed state, and thus, the metal plate and the electrode of thepiezoelectric body can be electrically connected to each other in thedispersed state in island shapes (anisotropic electrical conductivity),rather than electrical conduction over the entire surface (isotropicelectrical conductivity) as in the case of an electrically conductiveadhesive using conventional carbon black. More specifically, whileconductivity is provided in the direction in which the metal plate isopposed to the electrode, no conductivity is provided in the planardirection. This anisotropically conductive structure greatly improvesthe contact probability of the carbon black spectacularly, as comparedto a case in which the same or substantially the same amount of carbonblack in provided a dispersed state, thereby enabling a higherconductivity (lower resistance value) to be achieved. Furthermore, whenthe piezoelectric body is bonded to the metal plate, a fillet is formedby the electrically conductive adhesive around the piezoelectric body,and there is a possibility that short-circuiting may be caused if thefillet partially wraps around the upper electrode of the piezoelectricbody. The electrically conductive adhesive according to variouspreferred embodiments of the present invention has anisotropicelectrical conductivity, and thus, effectively and securely preventsthis short-circuiting.

While the electrically conductive adhesive according to variouspreferred embodiments of the present invention may preferably be anysolventless or solvent-based electrically conductive adhesive, at leastelectrically conductive adhesives using a water-based solvent areexcluded. The solventless electrically conductive adhesive refers to anelectrically conductive adhesive including carbon black that is added toa liquid resin, whereas the solvent-based electrically conductiveadhesive refers to an electrically conductive adhesive including carbonblack that is added to an organic solvent in which a polymer isdissolved. Solventless resins include, for example, an epoxy resin,whereas solvent-based resins include, for example, an acrylic resin. Ineach case, the hardened state is not porous, is less likely to causeswelling of the adhesive due to absorption of water in terms oflong-term reliability, and is free of the problem of decrease inconductivity.

The carbon black included in the electrically conductive adhesivepreferably has a nano-level average particle size, and is preferably,for example, carbon black with an average particle size of about 5 nm toabout 300 nm, for example. The carbon black is added to the resin sothat primary particles of the carbon black preferably form an aggregatewith an average particle size of about 1 μm to 50 μm, for example, inthe resin. Therefore, an appropriate dispersing/kneading treatment ispreferably performed so that the carbon black forms an aggregate with anintended particle size in the resin.

The metal plate and the electrode of the piezoelectric body arepreferably subjected to pressurization so that the distance between themetal plate and the electrode is less than the average particle size forthe aggregate. More specifically, the distance between the metal plateand the piezoelectric body is preferably less than the average particlesize for the aggregate in the electrically conductive adhesive in thepaste form. This distance sandwiches most of the aggregate between themetal plate and the electrode of the piezoelectric body, therebyenabling reliable electrical conductivity to be achieved.

The resin included in the electrically conductive adhesive is preferablya resin which has a dense composition in a hardened state, has highweather resistance and heat resistance, and is less likely to undergoswelling even in a humidity test after bonding. Specifically, the resinmay preferably be an epoxy resin, an acrylic resin, a urethane resin,other suitable resin, for example.

The amount of the carbon black in the electrically conductive adhesiveis preferably about 1 weight % to about 10 weight % with respect to thetotal amount of the carbon black and resin, for example. This lowcontent of the carbon black reduces the viscosity or thixotropy of theadhesive, thereby resulting in favorable workability and applicationproperty, and even with the low content of the carbon black, theformation of the aggregate can provide favorable electricalconductivity.

As described above, according to various preferred embodiments of thepresent invention, the electrically conductive adhesive in a paste formwhich has the carbon black added to a solventless or a solvent-basedresin so as to form an aggregate with an average particle size of about1 μm to about 50 μm is preferably used to apply the electricallyconductive adhesive between the metal plate and the electrode of thepiezoelectric body, and the metal plate and the piezoelectric body aresubjected to heating and pressurization to harden the electricallyconductive adhesive. Thus, the aggregate is deformed so as to follow theconcavity and the convexity of the metal plate and of the electrode ofthe piezoelectric body, thereby enabling outstanding conductivity to beprovided with less damage to the piezoelectric body and withoutsignificantly contributing to the increase in the thickness of theadhesive. In addition, since favorable electrical conduction is achievedwhile the content of the carbon black is reduced, the absolute amount ofthe resin can be increased, thereby resulting in a decrease in theviscosity or thixotropy of the adhesive, and in favorable workabilityand application property, and favorable adhesion can be achieved betweenthe metal plate and the piezoelectric body. Furthermore, since the resindoes not include any water, the hardened state is advantageously notporous, is less likely to cause swelling of the adhesive due toabsorption of water, and thus has a significantly improved long-termreliability.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a known example of a piezoelectric vibration plate whichincludes a piezoelectric body bonded to a metal plate.

FIGS. 2A to 2D are enlarged cross-sectional views illustratingconventional bonding structures.

FIGS. 3A and 3B are cross-sectional views of a bonding structureaccording to a preferred embodiment of the present invention before andafter heating and pressurization.

FIG. 4A is a diagram showing the relationship between an aggregate sizeand an adhesive viscosity, and FIG. 4B is a diagram showing therelationship between an aggregation size and an adhesive thickness.

FIG. 5 is a diagram for evaluating the conductivity in the case ofbonding two metal plates with the use of an electrically conductiveadhesive.

FIGS. 6A and 6B are diagrams for comparing the viscosity-thixotropy andseries resistance characteristics between a case of adding dispersedcarbon black and a case of adding aggregated carbon black.

FIG. 7 shows another example of a piezoelectric vibration plate whichincludes a piezoelectric body bonded to a metal plate with anintermediate plate interposed therebetween.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 3A and 3B show a bonding structure of a piezoelectric vibrationplate according to a first preferred embodiment of the presentinvention, where FIG. 3A shows the bonding structure before heating andpressurization and FIG. 3B shows the bonding structure after the heatingand pressurization. As in the case of FIG. 1, a piezoelectric body 2including electrodes 3, 4 on both sides thereof is bonded onto a metalplate 1, such as a diaphragm, with an electrically conductive adhesive10 interposed therebetween. The electrically conductive adhesive 10 ispreferably a paste including a solventless resin 11 such as, forexample, an epoxy resin including carbon black 12 a therein which has anaverage particle size of about 5 nm to about 300 nm, and preferablyabout 5 nm to about 100 nm, for example, added thereto, and the additiveamount of the carbon black 12 a is preferably about 1 weight % to about10 weight %, for example, with respect to the total amount of the carbonblack 12 a and resin 11. The carbon black 12 a is preferably primarilypresent in clusters in the resin 11 so as to form an aggregate 12 withan average grain size of about 1 μm to about 50 μm, for example, ratherthan present as primary particles in the resin 11. The aggregate 12refers to primary particles of the carbon black 12 a bonded by anintermolecular force to provide a size of about 1 μm or more, forexample.

Before heating and pressurization, as shown in FIG. 3A, the aggregate 12is floating in the resin 11, without making contact with the metal plate1 or the electrode 3. Therefore, the metal plate 1 is not electricallyconnected to the electrode 3. The lower content of the carbon black 12 aincluded in the electrically conductive adhesive 10 and the largeramount of the resin 11 reduces the viscosity-thixotropy of the adhesive,thereby resulting in favorable workability and application property.

When the metal plate 1 and the piezoelectric body 2 are subjected toheating and pressurization, the aggregate 12 is deformed so as to followthe concave-convex surfaces of the metal plate 1 and the electrode 3 asshown in FIG. 3B, and thus, is sandwiched between the metal plate 1 andthe electrode 3. Therefore, the metal plate 1 is effectively andsecurely electrically connected to the electrode 3. Since the carbonblack 12 a is hardened while remaining as the aggregate 12 rather thanin a dispersed state, the metal plate 1 and the electrode 3 of thepiezoelectric body 2 are electrically connected to each other atmultiple points in island shapes (anisotropic electrical conductivity).The electrically conductive structure with anisotropic conductivitygreatly improves the contact probability of the carbon black 12 a, ascompared to a case in which the same amount of carbon black 12 a is in adispersed state, thereby enabling a higher conductivity (a lowerresistance value) to be achieved.

In the case of FIG. 3B, when pressurization is performed so that thedistance d between the metal plate 1 and the piezoelectric body 2 isless than the average particle size of the aggregate 12, the metal plate1 and the electrode 3 can preferably not only be electrically connectedto each other with the aggregate 12 interposed therebetween, but canalso be directly connected to each other. Therefore, the conductivity isfurther improved for the both the metal plate 1 and the electrode 3. Itis to be noted that the distance d between the metal plate 1 and thepiezoelectric body 2 can be obtained as a value, in such a way that theregion (area) surrounded by the surface of the metal plate 1 and theelectrode 3 of the piezoelectric body 2 is divided by a predeterminedlength when the predetermined length is extracted in the horizontaldirection of FIG. 3B. More specifically, the distance d refers to theinterval between the position of the center line with respect to theprofile curve at the surface of the metal plate and the position of thecenter line with respect to the profile curve at the surface of theelectrode of the piezoelectric body.

FIG. 4A shows the relationship between the aggregate size and theadhesive viscosity, and FIG. 4B shows the relationship between theaggregate size and the adhesive thickness. It is to be noted that thecontent of the carbon black was about 3.0 weight %. As shown in FIG. 4A,the particle size of the aggregate less than about 1 μm sharplyincreases the viscosity of the adhesive, and the particle size of theaggregate is thus preferably about 1 μm or more, for example. On theother hand, as shown in FIG. 4B, the adhesive thickness increases withthe increase in the particle size of the aggregate, and in particular,the particle size greater than about 50 μm increases the rate ofincrease in adhesive thickness, and thus, makes vibrations of thepiezoelectric body less likely to be transmitted to the metal plate,thereby resulting in a degradation of product characteristics.Therefore, the average particle size of the aggregate is preferablyabout 1 μm to about 50 μm, for example.

FIG. 5 is a diagram for evaluating the conductivity in the case ofbonding two metal plates 20, 21 with the use of an electricallyconductive adhesive 22. For this evaluation, on the assumption that theadhesive thickness varies, the metal plates 20, 21 were bonded with theelectrically conductive adhesive 22 including insulating spacers 23having a diameter of about 3 μm interposed therebetween, so as toprovide a thickness of about 3 μm, and the series resistance wasmeasured between the metal plates 20, 21. The evaluation results areshown in Table 1. It is to be noted that the amount of the components inthe adhesive was about 3 weight % for carbon black and about 97 weight %for an epoxy resin. The carbon black (primary particles) had an averageparticle size of about 50 nm, the aggregate had an average particle sizeof about 5 μm, and spherical carbon had a particle size of about 3 μm.

TABLE 1 Electrically Conductive Adhesive Carbon Dispersed AggregatedSpherical Free Carbon Carbon Carbon Series 7500 105 10 100 Resistance(Ω)

As is clear from Table 1, when using aggregated carbon black accordingto preferred embodiments of the present invention, the series resistanceis dramatically low, as compared to when no carbon black is included,and furthermore, the resistance value can be reduced to about 1/10 orless as compared to when the dispersed carbon black or the sphericalcarbon is included. More specifically, the electrical conductivity isdramatically improved.

FIGS. 6A and 6B are diagrams for comparing the viscosity-thixotropy andseries resistance characteristics between a case in which dispersedcarbon black is added and a case in which aggregated carbon black isadded. FIG. 6A is a diagram showing the relationship between theadditive amount of carbon black and the viscosity-thixotropy, where thechange in viscosity-thixotropy is smaller with respect to the additiveamount of carbon in the case of the aggregated carbon black, as comparedto the dispersed carbon black. Therefore, when an allowable line L1 isset for the viscosity-thixotropy, the additive amount of carbon can befurther increased for the aggregated carbon black as compared to thedispersed carbon black. In addition, when a comparison is made with thesame additive amount of carbon, the aggregated carbon black has lowerviscosity-thixotropy, and thus, provides favorable application stability(variations in the amount of application, leveling properties after theapplication) in the step of applying the adhesive. On the other hand, asshown in FIG. 6B, there is an inverse relationship between the additiveamount of carbon black and the series resistance, and when apredetermined allowable line L2 is set, a smaller amount of theaggregated carbon black achieves a desirable resistance value. Morespecifically, the additive amount of the aggregated carbon black can bereduced to a greater extent when the same viscosity or resistance valueis to be achieved. Therefore, the cost is reduced.

As described above, the advantageous effects of the bonding structureaccording to preferred embodiments of the present invention aresummarized as follows.

Since the aggregate of carbon black is deformed in a flexible manner, anincrease in thickness is less affected by the adhesive.

Since the aggregate of carbon black is deformed in a flexible mannerduring bonding by pressurization, damage to the piezoelectric body isprevented or minimized.

Since the carbon black is present as aggregates (in clusters), thecontact probability of the carbon black is greatly improved, and ahigher conductive effect (anisotropic conductivity) is achieved ascompared to the case in which the same amount of carbon black is presentin a non-aggregated (primary particle) state.

Since the electrically conductive adhesive has anisotropic conductivityin the bonded state, short-circuiting s prevented even when a filletformed around the piezoelectric body partially wraps around theelectrode at the surface.

The reliability of electrical conductivity is improved because theflexible deformation of the carbon black aggregate more effectivelyresponds to a swelling adhesive in a humidity test.

As compared to primary particles of carbon black dispersed in a resin,the fluidity of the resin is greater, and the influence on theviscosity-thixotropy is substantially suppressed.

The bonding structure according to preferred embodiments of the presetinvention is not limited to the structure with the piezoelectric body 2directly bonded onto the diaphragm 1 as shown in FIG. 1, and may be astructure in which a metallic intermediate plate 8 is bonded on thediaphragm 1 and the piezoelectric body 2 is bonded thereon as shown inFIG. 7. In this case, the electrically conductive adhesive 10 accordingto a preferred embodiment of the present invention is disposed betweenthe diaphragm 1 and the intermediate plate 8 and between theintermediate plate 8 and the piezoelectric body 2, and because theelectrically conductive adhesive 10 is highly conductive and providesexcellent adhesion as described above, favorable conductivity andbonding properties are ensured among the electrode 3 of thepiezoelectric body 2, the intermediate plate 8, and the diaphragm 1. Inthe bonding structure according to preferred embodiments of the presentinvention, the metal plate and the piezoelectric body may have anysuitable shape, such as a disk shape, a quadrangular plate shape, or anannular shape, for example. The piezoelectric vibration plate accordingto preferred embodiments of the present invention can be used not onlyfor piezoelectric microblowers for the transportation of compressiblefluid such as air, but also for piezoelectric fans, piezoelectricmicropumps for the transportation of incompressible fluid such as water,piezoelectric speakers, piezoelectric buzzers, piezoelectric sensors,and other suitable piezoelectric devices, for example.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A bonding structure comprising: a metal plate; apiezoelectric body including an electrode provided on a side of thepiezoelectric body opposed to the metal plate; and an electricallyconductive adhesive including carbon black as an electrically conductiveaid and bonding the metal plate and the electrode of the piezoelectricbody to one another so as to provide electrical conductivitytherebetween; wherein the electrically conductive adhesive beforehardening includes carbon black having a nano-level average particlesize, and is in a paste form in a solventless or solvent-based resin sothat the carbon black forms an aggregate with an average particle sizeof about 1 μm to about 50 μm; and the bonding structure is configured byapplying the electrically conductive adhesive in the paste form betweenthe metal plate and the electrode of the piezoelectric body, subjectingthe metal plate and the piezoelectric body to heating and pressurizationto deform the carbon black aggregate, and hardening the electricallyconductive adhesive.
 2. The bonding structure according to claim 1,wherein the metal plate and the piezoelectric body are subjected topressurization so that a distance between the metal plate and theelectrode of the piezoelectric body is less than the average particlesize of the aggregate.
 3. The bonding structure according to claim 1,wherein the electrically conductive adhesive in a hardened state hasanisotropic conductivity.
 4. The bonding structure according to claim 1,wherein an amount of the carbon black in the electrically conductiveadhesive is about 1 weight % to about 10 weight % with respect to atotal amount of the carbon black and the solventless or solvent-basedresin.
 5. A bonding structure comprising: a metal plate; a piezoelectricbody including an electrode provided on a side of the piezoelectric bodyopposed to the metal plate; and an electrically conductive adhesiveincluding carbon black as an electrically conductive aid and bonding themetal plate and the electrode of the piezoelectric body to one anotherso as to provide electrical conductivity therebetween; wherein thecarbon black forms an aggregate with a nano-level average carbon blackparticle size, so that the aggregated carbon black average particle sizeis about 1 μm to about 50 μm; the aggregated carbon black is sandwichedbetween the metal plate and the electrode and deformed so as to follow aconcave-convex surface of the metal plate and the electrode; and themetal plate and the electrode of the piezoelectric body are electricallyconnected to each other at multiple points in island shapes.